A gas diluting and testing apparatus is used to analyze, among other things, vehicular exhaust. The apparatus uses a mixing system to dilute the exhaust gasses so that the moisture content of the gasses is sufficiently reduced in order to minimize errors due to condensation. One example of an existing mixing system is the constant volume sampler (CVS).
The CVS has been used for over twenty-five years to sample the emissions from automobiles. It is the device used for automotive emissions tests that are the basis for the certification that vehicles sold in the United States are compliant with the Clean Air Act.
Automotive sampling systems, as well as other analytical systems, utilize sealed bags for collecting engine exhaust gasses for analysis of components after the collection interval has been completed. In order to preserve the integrity of the captured sample, the sample bag material must be inert, non-reactive, without leaks, and must have low permeation for the specific gasses contained both within the bag and outside the bag. The sample bag must not emit or absorb gasses, and the bag material must be flexible for fill and empty cycling. In the past, materials used for construction of the sample bag walls have failed to meet one or more of the above criteria, and it is desirable to provide a sample bag that limits these various undesirable characteristics. As vehicles become cleaner, their emissions become more difficult to measure accurately. To overcome some of the inherent limitations of the CVS, some attempts have been made to develop improved mixing systems. In addition to the effects of the mixing system itself, mixing systems that collect a gas mixture with a sample bag may sometimes be limited in accuracy due to limitations of the sample bag.
Although many existing mixing systems and existing sample bags have been used in applications that are commercially successful, with increasing demands for more accurate measurement techniques, it is desirable to make improvements to existing measurement and dilution techniques for analysis of gaseous constituents.